CHENGDU, China  The construction boom that has turned China into the world’s largest consumer of energy, and largest emitter of carbon pollution linked to climate change, is on dramatic display in Tianfu New Area.

Erected in little more than a decade, this outcropping of office parks and high-rise apartments already rivals its parent city, the 2,100-year-old metropolis of Chengdu.

The largest building on the planet opened here in January: a steel-and-glass pagoda enclosing 1.7 million square meters of floor space. The New Century Global Center, as it is called, is about the size of three Pentagon buildings.

Below ground lies the inaugural subway line for a nine-rail network that’s expected to be done by 2020. And plans are being laid for Chengdu’s second international airport.

China’s rapid urbanization and industrialization are powered primarily by coal, which produces twice as much carbon dioxide per unit of energy as natural gas. Coal provides for 70 percent of China’s energy needs. Coal forges China’s steel and fertilizes its fields.

That dependency on “dirty energy” has come under increasing scrutiny in recent weeks — in China and abroad — as China’s smog-choked northeastern cities have forced the closure of schools for health reasons and airports because of poor visibility.

The scale of China’s growing energy needs, and associated environmental challenges, dwarfs clean-energy gains in the United States.

Energy-related carbon emissions in the U.S. are at their lowest level since 1994 as natural-gas generation has edged out coal and vehicles have made steady gains in fuel efficiency.

Meanwhile, China has become a voracious importer of fossil fuels, said David Fridley, a staff scientist with the China Energy Group at the Lawrence Berkeley National Laboratory.

Infrastructure building

When it comes to energy, the popular image of China as a manufacturing outpost for the world’s consumer goods misses the mark, said Fridley, a lead editor of an authoritative almanac on China’s energy use and production.

Most of the Chinese economy is dedicated to building up the country’s infrastructure.

“They have urbanized the (equivalent of the) entire population of the U.S. in the last 20 years, and will do it again in the next 20 years. ... They’re now at a point where they realize they can’t continue doing it forever,” he said.

International coverage

U-T San Diego reporter Morgan Lee recently visited New York, Japan and China through a fellowship with the East-West Center, which was established by the U.S. Congress to promote better understanding among people in the United States, Asia and the Pacific.

Central planners are encouraging a gradual cooling off for the construction sector, as concerns emerge about excess industrial capacity, overleveraged debts and lack of coordination that has left some newly constructed cities vacant.

Airborne pollution

In early October, an acrid smog settled over Chengdu — though nowhere near as thick as the pollution afflicting the northeast.

Along central avenues in the metropolitan area of 14 million residents, buses and cars mingled with swarms of electric scooters, bicycles and the occasional horse-drawn cart. Airborne pollution in subtropical Chengdu is less the consequence of China’s transportation sector than construction and heavy industry — and the power plants that sustain them.